In U.S. Pat. No. 2,397,069 to F. M. Young et al, issued Mar. 19, 1946, it was found to be desirable to have supplemental coolers for cooling selected fluids, such as transmission oil, and the like. Young et al recognized that a supplemental cooler could be piggybacked or tandemed onto the radiator cooling system. This arrangement had the problem of overstressing the joints between the parts of the cooling system causing leaks and failures. It also required that the cooling system had to be disassembled to service the supplemental heat exchanger. The added cooler added size to the structure making it unusable in certain applications.
In U.S. Pat. No. 2,796,239 to J. R. Holmes et al, issued June 18, 1957, another system was proposed wherein a separate cooler was mounted directly on the element itself, such as on the transmission housing, wherein cooling fluid was piped from the radiator to the cooler. This system had the disadvantage of the added cost for the extra cooler and piping plus the problems with leaky piping and the like.
U.S. Pat. No. 3,096,818 to H. W. Evans et al, issued July 9, 1963, shows an ebullient cooler wherein steam is admitted to the system for condensing. Engine oil is passed through the lower tank of the cooler to maintain the oil at a uniform temperature. A complex system of baffles, and the like, are provided particularly in the upper tank for condensing the steam and controlling the flow of the condensate.